Three others were also hurt in the blast that occured at about 2.45pm (1245 GMT) in Pratteln, about 10km south-east of the city that borders France and Germany.
One victim was airlifted to hospital for treatment following the explosion which destroyed part of a four-storey building, and the injured had lain buried under the rubble.
It was not clear how many of the apartment block’s 34 residents were at home when the explosion struck.
Dozens of firefighters, ambulance staff and police rushed to the site, where police said gas was almost certainly the cause of the blast.
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